Hypoxia increases thrombospondin-1 transcript and protein in cultured endothelial cells

The exposure of endothelial cells to hypoxic environments regulates the exp ression of a number of genes with products that are vasoactive or mitogenic for vascular tissue, including platelet-derived growth factor, endothelin- 1, and endothelial nitric oxide synthase. Hypoxia is also known to alter th e adhesive properties of endothelium toward a variety of blood cell types. Thrombospondin-1 (TSP-1) is a glycoprotein with major roles in cellular adh esion and vascular smooth muscle proliferation and migration. We report her e that hypoxia induces TSP-1 gene and protein expression. Oxygen tensions o f less than or equal to 30 torr resulted in TSP-1 transcript induction init ially apparent at 1 to 6 hours, with maximal induction (6.5-fold +/- 1.2-fo ld) within 24 to 48 hours in both human and bovine endothelial cells. TSP-1 protein levels remain elevated after 72 hours of continuous hypoxic exposu re. The induction of TSP-1 steady-state transcript levels is caused in larg e part, if not entirely by post-transcriptional stabilization of the TSP-1 mRNA. The TSP-1 induction by hypoxia is a graded and reversible physiologic response and can be mimicked by the use of cobalt chloride or the inhibiti on of nitric oxide production, suggesting both the involvement of a heme-co ntaining oxygen sensor and a role for the endogenous production of nitric o xide in TSP-1 regulation. The effects of hypoxia both on the stabilization of the TSP-1 transcript and the stimulation of TSP-1 protein production are completely inhibited by arginine butyrate.